226b89f846
Set license to multi-license of AGPL + Element Commercial, and add associated license files to the repository root. This does not add a notice of "This file includes modifications" to any files because they were only moved and relicensed, but otherwise unmodified. The exception is run_in_venv.sh, which is a rewrite of upstream's run_in_venv.js and thus lacks the original copyright entirely.